The invention relates to optical communication, and, more particularly, to variable wavelength optical filters for use in optical communications.
A leading technology for use in next generation high-speed communication networks has been wavelength division multiplexing (WDM) or its variations such as Dense-WDM. See, e.g., M. S. Borella, J. P. Jue, D. Banerjee, et al., “Optical Components for WDM Lightwave Networks,” Proceedings of the IEEE, Vol. 85, No. 8, pp. 1274–1307, August 1997, the contents of which are incorporated by reference herein. In a WDM system, multiple signal sources are emitted at different wavelengths and multiplexed onto the same optical medium, each wavelength representing a separate channel. Due to the dynamic change of traffic patterns and the demand for intelligent switching, it is advantageous to incorporate capabilities to select a specific channel or range of channels from the multiple wavelength bands carried by the optical network. Accordingly, tunability has been one of the most important challenges in a WDM optical network.
Conventional tunable filters have employed a range of techniques, such as Fabry-Perot interference, Mach-Zehnder interference, thin film interference, etc. See, e.g., J. M. H. Elmirghani, H. T. Mouftah, “Technologies and Architectures for Scalable Dynamic Dense WDM Networks,” IEEE Communications Magazine, pp. 58–66, February 2000; D. Sadot and E. Boimovich, “Tunable Optical Filters for Dense WDM Networks,” IEEE Communications Magazine, p. 50–55, December 1998, which are incorporated by reference herein. Unfortunately, while conventional tunable filters have proven to be flexible in the selection of the wavelength of the passband (single channel or waveband) from the input optical signal to pass through, the width of the passband (number of channels) on the other hand has generally been fixed. Recently, more complicated solutions have been suggested and implemented, such as what are commonly referred to as “wavelength selective switches” (WSS). See, e.g., U.S. Patent Application Publication 2002/0186434, Ser. No. 10/140,116, the contents of which are incorporated by reference herein. Although highly flexible in their switching and tuning capabilities, wavelength selective switches are, in general, expensive and often have limited scalability.
Accordingly, there is a need for an approach that is more flexible than existing tunable filters but that is also more inexpensive and scalable than existing wavelength selective switch architectures.